The hands-on activities in this lesson will help students understand how plants and their roots help slow the erosion process.
Main Curriculum Tie:
Science - 4th Grade
Standard 3 Objective 2
Explain how the processes of weathering and erosion change and move materials that become soil.
- Erosion and Rocks and Soil, by Bill Nye
Background For Teachers:
Rocks and other materials on Earth’s surface are constantly subjected
to the powerful forces of weathering, erosion, transport, and deposition. Weathering is the breakdown of rock and other materials into smaller
pieces. Erosion is the removal of those smaller pieces of rock and soil.
Transport moves these pieces, and deposition is the dropping off or
depositing of those materials in a new location.
Rocks can be broken down by physical or chemical weathering. Physical weathering is the cracking, breaking up, and grinding down of
rocks into smaller pieces while maintaining the same mineral
composition. This type of weathering is caused by a number of different
factors. Changing temperatures cause rocks to crack and flake, ice splits
rocks open, living things dig or pry open rocks, gravity causes rocks to
fall and shatter, and abrasion breaks down rocks with solid particles like
Chemical weathering is the breakdown of rocks as a result of a
change in their mineral composition. In this type of weathering, minerals
can either be added to or removed from rocks. Water and acids are the
major destructive agents of chemical weathering because they can
dissolve minerals that hold rocks together by chemically changing the
rock and causing it to crumble. Acid rain, plant acids, carbonation, and
oxidation can cause chemical weathering. Erosion, the transportation of
weathered materials, and deposition, the deposit of these materials in a
new location, are processes that often occur together. Erosion and
deposition can be caused by various factors. Gravity pulls rocks down
slopes, wind and running water pick up and carry loose materials, waves
fragment the shoreline, and glaciers erode and carve away land as they
Weathering and erosion are two of the most important concepts in
geology. They affect the landscape that we live on and are important in
the formation of soil.
Over time, humans have learned techniques to minimize the effects of
these three forces of nature to preserve land formations and soil, which is
a valuable resource. Soil erosion can be slowed down by plant growth
covering bare soil. This is accomplished in two ways: 1) the roots hold
the soil in place, and 2) the vegetation absorbs the impact of the water
hitting the ground, lowering the velocity with which the water enters the
Intended Learning Outcomes:
1. Use Science Process and Thinking Skills
4. Communicate Effectively Using Science Language and Reasoning.
Invitation to Learn
Ask: What is soil erosion? How does soil move? What can be done
to help keep it where it is needed?
- Divide the students into small learning groups (four to five
students) and distribute the materials.
- Instruct the students to place the soil in the center of their Splashdown Target.
- One student in each group should fill a pipette with water.
Holding the pipette approximately two to three centimeters
above the soil, drop ten droplets of water onto the soil.
- Count the number of droplets that have splashed into outlying
zones on the target. Record this number on a tally sheet.
- Pass the pipette to another student in the group. The new
student will hold the pipette approximately five to six
centimeters above the soil (or twice the height as before) and drop
ten droplets of water onto the soil.
- Observe and record the number of splashes on a tally sheet.
- Pass the pipette to the next student, who drops water from twice
the height of the previous drop. Record the results.
- Once again, pass the pipette to the remaining one or two students
in the group, holding the pipette twice as high as the previous
student. Drop ten droplets of water on the soil. Observe and
record the results.
- Ask each group to answer the following questions in a journal:
- What did you observe happening?
- What color are the droplets of water and why are they that
- What results were observed as the pipette was raised?
- Write a hypothesis about what they believe will happen if the
pipette is raised even higher.
- Write a hypothesis about what they think happens when a
raindrop falls onto the soil.
- Wash the Splashdown Targets and place a grass plug in the center
of the target.
- Repeat steps #3 to 9.
- Discuss with the class the following information:
- None of the water splashed off the dry soil when the first
water droplets were dropped.
- The soil needed to become saturated before any splashes
occurred. When the soil became saturated and could hold no
more water, the droplets started to splash onto the target.
- The drops were brown because some of the soil was being
carried away with the water. This is erosion.
- As the water was dropped from a higher point, the splashes
became more prolific, covering a larger area. This is because
of the increased velocity of the water droplets. Raindrops hit
with a great velocity because of the speed they are able to
obtain as they fall through the atmosphere.
- The grass plug helped slow the process of erosion in two
- the roots helped hold the soil in place, and
- the blades of grass absorbed the force of the falling water
droplet, allowing the water to trickle into the soil instead
of blasting it.
Measure the splashes to the nearest centimeter. Make a graph
showing the results of the number of splashes in each zone at
Identify local areas that are prone to soil erosion.
- Encourage students to survey their yards and surrounding
neighborhoods for signs of soil erosion. Have them discuss with
family members ways in which vulnerable areas could be
- Each student should have completed a journal answering the five
questions in procedure #9 for the soil water drop and the grass
plug water drop. S/he should be able to communicate two ways
in which plants help slow the process of erosion.
Created Date :
Oct 19 2004 11:46 AM